This invention relates, in general to an air induction control device for an internal combustion engine, which controls air to be inducted to an intake passage downstream of a closed throttle valve, and more particularly to an air induction device functioning to supply air into the combustion engine both continuously during a normal engine deceleration and temporarily at a sudden engine deceleration or during operation of engine accessories at idle throttle state.
In connection with air induction control in an internal combustion engine, when a throttle valve is maintained at its idle position, for example, during a relatively long period engine deceleration, an extremely high vacuum is kept for a long period of time in an intake passageway downstream of the throttle valve. As a result, engine oil may be sucked into a combustion chamber through a clearance between a cylinder surface and a piston, which increases engine oil consumption. As will be apparent, this problem rises at a relatively high vacuum prevailing in the intake passageway downstream of the throttle valve.
Furthermore, when the throttle valve is abruptly closed from its high speed position, for example, during a sudden engine deceleration, the vacuum in the intake passageway downstream of the throttle valve abruptly increases by the pumping action of the piston. As a result, fuel adhered on the surface of the intake passageway may be vaporized in a moment so as to temporarily supply the combustion chamber of the engine with over-rich air-fuel mixture which will give rise to misfire. This over-rich air-fuel mixture causes the engine to produce unburned combustible gas which may result in so-called backfire in which the combustible gas drastically burns with sound in an exhaust conduit. Additionally, in using engine accessories such as an air conditioner and a power steering system air, engine stall may occur during operation of the engine accessories at idling. As such, it is required to increase idle engine speed under such a condition. Such problems at the rapid deceleration and during operation of engine accessories rise at a relatively low vacuum prevailing in the intake passageway downstream of the throttle valve.
In order to solve the above-mentioned two kinds of problems raised at the relatively low and high vacuum prevailing in the intake passageway downstream of the throttle valve, two separate devices are, in conventional techniques, installed at an intake system of the engine by which air is introduced into the engine bypassing the throttle valve when the vacuum prevailing in the intake passageway downstream of the throttle valve exceeds a predetermined level and a predetermined higher level. As such, engine layout becomes complicated, increasing engine weight. Additionally, such devices require complicated pipings using a large number of rubber hoses etc. and accordingly are liable to raise accidents such as hose breakages, hose disconnections, and air leaks from hose connections. This unavoidably needs troublesome service for maintenance.